largefiles: reset "lfstatus" attribute to previous value in "finally"

We were resetting it to False, which means nesting of these overrides
would be incorrect.

Differential Revision: https://phab.mercurial-scm.org/D7137

hgext/largefiles/overrides.py

@@ -160,11 +160,12 b' def addlargefiles(ui, repo, isaddremove,'
 
 @contextlib.contextmanager
 def lfstatus(repo):
+    oldvalue = getattr(repo, 'lfstatus', False)
     repo.lfstatus = True
     try:
         yield
     finally:
-        repo.lfstatus = False
+        repo.lfstatus = oldvalue
 
 
 def removelargefiles(ui, repo, isaddremove, matcher, uipathfn, dryrun, **opts):